Quarterly Financial Information (Summary Of Quarterly Financial Information) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended										12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013		Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012		Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Quarterly Financial Data [Abstract]
Net premiums earned	$ 680,892	$ 678,913	$ 675,787		$ 662,595	$ 655,777	$ 646,084		$ 637,247	$ 635,812	$ 2,698,187	$ 2,574,920	$ 2,566,057
Change in fair value of investments pursuant to the fair value option	(30,593)	21,815	(78,726)		43,467	(28,944)	44,783		(24,788)	49,343	(44,037)	45,509	31,289
Income (loss) before income taxes	11,268	54,793	(24,959)		90,994	(39,161)	91,330		(18,853)	101,994	132,096	135,310	245,099
Net income	$ 15,376	$ 39,570	$ (9,264)		$ 66,461	$ (17,382)	$ 66,201		$ (5,264)	$ 73,356	$ 112,143	$ 116,911	$ 191,164
Basic (in dollars per share)	$ 0.28	$ 0.72	$ (0.17)		$ 1.21	$ (0.32)	$ 1.21		$ (0.10)	$ 1.34	$ 2.04	$ 2.13	$ 3.49
Diluted (in dollars per share)	$ 0.28	$ 0.72	$ (0.17)	[1]	$ 1.21	$ (0.32)	$ 1.21	[1]	$ (0.10)	$ 1.34	$ 2.04	$ 2.13	$ 3.49
Dividends paid per share	$ 0.6150	$ 0.6125	$ 0.6125		$ 0.6125	$ 0.6125	$ 0.61		$ 0.61	$ 0.61	$ 0.6150	$ 0.6125

[1] The dilutive impact of incremental shares is excluded from net loss position in accordance with GAAP.